The invention is generally related to fuel cells. More particularly, the invention is related to barrier coatings for interconnects, e.g., interconnects for solid oxide fuel cells. The invention is also related to a method of forming barrier coatings for interconnects, and devices made therefrom.
Chromium (Cr) containing electrical conductors such as ferritic stainless steels are widely used as interconnect (IC) materials in solid oxide fuel cells (SOFCs), because of their excellent oxidation resistance. These materials have the advantage of typically forming a thin Cr-rich oxide scale that protects the electrical conductors from rapid oxidation. The fuel cells also include a cathode; and the cathode materials often include strontium-based compositions such as lanthanum strontium ferrite, lanthanum strontium managanite, and lanthanum strontium cobalt ferrite.
One of the most commonly observed problems in solid oxide fuel cells utilizing these materials is the decrease in the performance of the cell on continuous usage. One of the reasons for degradation of performance is Cr-poisoning of the cathode. Cr from the oxide scale is known to migrate into the cathode and become deposited on active electrochemical sites, where reaction between oxygen, the cathode, and the electrolyte would normally take place. This type of reaction can degrade the performance of the device. Another cause of performance degradation in solid oxide fuel cells is the formation of low conductivity strontium chromate at the interface between the interconnect and the cathode layers. Strontium chromate forms as a result of the reaction of chromium, from the interconnect material, with strontium, which is depleted from the cathode layer. The thickness of the formed strontium chromate layer can increase during the prolonged or intermittent operation of the solid oxide fuel cell, and thereby degrade the performance of the device.
Therefore, it is desirable to reduce or eliminate at least some of the degradation mechanisms discussed above, so as to provide solid oxide fuel cells with better performance capability and improved life cycles. It would also be desirable to develop methods to fabricate solid oxide fuel cells having better performance.